This invention relates to a change-over valve means for a hydraulic clutch of a marine propulsion unit and more particularly to an improved rotary plug type valve.
Hydraulic valves are employed for a wide variety of purposes and a rotary plug type valve is a type of valve that is used quite frequently. One example in which such a valve is employed, is in the clutch actuating system for a marine outboard drive. Such a system includes a bevel gear transmission that incorporates clutches for selectively clutching one or another of counter rotating bevel gears for rotation with a shaft to drive the shaft in selected forward or reverse directions.
Conventionally, some form of fluid pump is provided for selectively pressurizing the fluid and a control valve distributes the pressurized fluid to a selected one of the clutches for its actuation while, at the same time, dumping the pressure in the other clutch. A rotary type plug valve, as will be latter described, is normally employed for this purpose. However, rotary type plug valves have certain disadvantages.
In the first instance, a rotary plug valve normally has a large diameter cylindrical body that is supported for rotation in a valve housing for controlling the distribution of fluid under pressure. Normally the fluid is admitted to the plug valve through an axially extending bore that opens through one end of the valve and which is intersected by a radially disposed delivery port. The fluid pressure admitted to the valve always acts against the end of the valve and hence exerts an axial force acting against an end housing. Although thrust bearings are normally employed so as to facilitate rotation of the valve, the large fluid pressure acting on the valve due to the large area across which the pressure reacts can give rise to difficulties in operating the valve.
In addition to these difficulties, the radially extending delivery port also gives rise to a radial reactive force on the valve element which tends to cause it to bind against the cylindrical wall of the housing and further makes rotation of the valve difficult.
It is, therefore, a principal object to this invention to provide an improved rotary plug type valve.
It is a further object to this invention to provide a rotary plug type valve in which the axial forces acting on the valve are substantially minimized.
It is a further object to this invention to provide a rotary plug type valve in which radial forces on the valve are eliminated or balanced.